The View Controllers are very important for our application. The user interacts with our application through them. A nice design is always the key to success when you're building apps, that is when the application works. Remember, if your app has severe bugs or most of the features are working erratically, no amount of good design choices in your View Controllers will help. The View Controllers are working very closely with your code so that the user interaction is interpreted by the application and the user gets a nice feedback/action happening on the screen.
The key to a good looking View Controller is a correct color scheme. Don't mix and match colors that simply won't go well together, and don't over-exaggerate with the colors.
Make the View Controllers clear, easily navigable, and easily understandable for the user. Having buttons that do various stuff is a great idea. Don't force everything on a single View Controller. Keep it clean.
You can check out some articles about good UI Design practices and color matching below.